Steam boiler plants are commonly constructed of gas tight tube banks forming walls supported on the outside thereof by a buckstay arrangement of flanged girders that extend around the boiler to prevent "dishing" of the walls as effected by a differential of pressure. Although a certain amount of thermal expansion of the tube walls is permitted with existing apparatus, the tube walls together with the buckstays frequently become over-stressed and fail because of a positive connection therebetween. Some arrangements with a sliding support as shown by U.S. Pat. No. 3,301,225 have been developed; however, in such an arrangement the sliding support permits restricted longitudinal movement only, while welded connections preclude other movement. Other arrangements exemplified by U.S. Pat. No. 3,203,376 have been developed whereby the forces exerted on the tube walls are transmitted to the surrounding buckstays by a combination of positive connections and pivotal linkages. Although such arrangements have been considered satisfactory for small furnaces that operate at low pressures, they lack flexibility, they are slow to construct, they require an excessive amount of handwork to assemble and to adjust, and they are, consequently, quite expensive to install and use.